1. Field of the Invention
The present invention relates to a mixer circuit for converting an input signal in SHF band into an output signal in UHF band, or converting an input signal in UHF band into an output signal in SHF band.
2. Description of the Prior Art
For a mixer circuit which is formed of a planar circuit employing a micro strip line and converts a high frequency signal into an intermediate frequency signal, is well known such a circuit employing a rat race circuit as shown in FIG. 1 of the accompanying drawings. The rat race circuit itself is disclosed in a Japanese Patent registration No. 214252 (published on Mar. 7, 1955). In FIG. 1, reference numeral 1 designates a rat race circuit having length nearly equal to three halves of the wavelength of each of a high-frequency input signal and a local oscillation signal. When the local oscillation signal is applied to an input terminal 2 of the rat race circuit 1, the signal is divided in two equal parts which are applied respectively to diodes 3 and 4 with a phase difference of 180 degrees. The high frequency input signal applied to an input terminal 5 is divided into two equal parts which are applied respectively to the diodes 3 and 4 in phase with each other. An intermediate frequency signal produced by the diodes 3 and 4 which has a frequency equal to the difference frequency between the high-frequency input signal and local oscillation signal, is outputted from an intermediate-frequency-signal outputting line 9 provided with stubs 7 and 8 which have a short-circuit impedance for the high-frequency input signal and local oscillation signal, since the rat race side of the diodes 3 and 4 is grounded through a circuit 6 having an inductive impedance. Though the above mixer employing the rat race circuit has an advantage that the local oscillation signal does not appear on the input terminal 5 which receives the high frequency signal, the mixer has drawbacks that a multilayered wiring 10 is required to fabricate the intermediate-frequency-signal outputting line 9, that the size of the mixer becomes large since the length of the rat race circuit is nearly equal to three halves of the wavelength of each of the input signal and the local oscillation signal, and that it is not possible to arrange the input and output lines freely because of the predetermined shape of the rat race circuit.